Retinoic acid-induced changes in polysialyltransferase mRNA expression andNCAM polysialylation in human neuroblastoma cells

Polysialic acid (PSA) is a dynamically regulated carbohydrate modification of the neural cell adhesion molecule NCAM, which is implicated in neural di fferentiation and cellular plasticity. The cloning and characterization of two polysialyltransferases, termed ST8SiaII (STX) and ST8SiaIV (PST), opene d up new perspectives in the search for factors that control this unique ce ll surface glycosylation. In vitro and transfection approaches revealed tha t ST8SiaII and ST8SiaIV are independently capable of synthesizing PSA on NC AM with slightly different specificities towards the major NCAM isoforms an d glycosylation sites. Their overlapping but distinct expression patterns d uring brain development point towards an independent transcriptional regula tion. However, the factors driving their joint or distinct expression, as w ell as the significance of divergent expression patterns in vivo, are not y et understood. In the present study, the mRNA expression of ST8SiaII and ST 8SiaIV was comparatively analyzed in neuronal differentiation of PSA-positi ve human neuroblastoma cell lines induced by retinoic acid (RA), phorbolest er, or growth factors. Using a semiquantitative RT-PCR strategy, we demonst rated a general decrease in the mRNA level of ST8SiaII upon differentiation of SH-SY5Y and LAN-5 cells. In contrast, a drastic increase of ST8SiaIV wa s specifically induced by RA-treatment of SH-SY5Y cells. To explore the sig nificance of these changes, the cellular capacity to perform PSA synthesis and the degree of NCAM polysialylation were analyzed. Our data indicate tha t the increased expression of ST8SiaIV enables an accelerated polysialylati on of NCAM, which, however, is not converted into higher amounts of PSA. (C ) 2000 John Wiley & Sons, Inc.